Fuel injection system

ABSTRACT

A fuel injection system for internal combustion engines has at least one fuel injector ( 4 ) which injects fuel into a combustion chamber ( 7 ) with a spark plug ( 3 ) projecting into the combustion chamber ( 7 ). The fuel injector ( 4 ) has a valve body ( 10 ) which has a plurality of injection holes ( 11, 11   d ) situated on the circumference. The injection holes ( 11, 11   d ) are designed so that a conical spray jet ( 5 ) is produced in the combustion chamber ( 7 ). At least the injection holes ( 11   d ) situated directly on both sides of the spark plug ( 3 ) have an elongated cross section.

BACKGROUND INFORMATION

[0001] The present invention relates to a fuel injection systemaccording to the definition of the species of claim 1 and claim 9.

[0002] In internal combustion engines having spark ignition of acompressed fuel mixture with internal formation of the mixture, a“mixture cloud” which must have a certain fuel-air ratio in theignitable range is required for stratified charge operation in the sparkplug area. To this end, fuel injectors having nozzles which open towardthe inside or the outside and produce a conical jet are used.

[0003] For example, German Patent Application 198 04 463 A1 describes afuel injection system for internal combustion engines having sparkignition of a compressed fuel mixture; this fuel injection system isprovided with at least one fuel injector which injects fuel into acombustion chamber formed by a piston/cylinder arrangement and isequipped with a spark plug projecting into the combustion chamber. Thenozzle body of the fuel injector is provided with at least one row ofinjection holes distributed over the circumference of a nozzle body ofthe fuel injector. Through controlled injection of fuel through theinjection holes, a jet-guided combustion method is implemented by theformation of a mixture cloud, at least one jet being directed in thedirection of the spark plug. Other jets ensure that an at leastapproximately closed or coherent mixture cloud is formed.

[0004] German Patent 196 42 653 C1 describes a method of forming anignitable fuel-air mixture. An ignitable fuel-air mixture is formable inthe cylinders of direct-injection internal combustion engines, in thatfuel is injected into each combustion chamber delimited by a piston, byway of an injector on opening of a nozzle orifice due to a valve elementbeing lifted up from a valve seat surrounding the nozzle orifice. Topermit formation of a mixture optimized for fuel consumption andemissions in each operating point of the entire engine characteristicsmap under all operating conditions of the internal combustion engine, inparticular in stratified charge operation, the opening stroke of thevalve element and the injection time are adjustable.

[0005] German Patent 38 08 635 C2 describes a fuel injection device fordirect injection of fuel into the cylinder of an internal combustionengine having compression of a fuel mixture. The fuel injection deviceincludes a fuel injector which is situated in the cylinder wall at adistance from the cylinder head and opposite the exhaust opening andwhich has an outlet opening, with the axis of the jet of the injectionvalve being directed at the area around the spark plug situated in thecylinder head. The fuel injector here has a magnetically operated valveneedle having helical swirl grooves to produce a swirl flow of theinjection jet. The total cross-sectional area of the swirl grooves issmaller by at least one half than the cross-sectional area of the outletopening, the fuel injector being situated above the flushing opening,and with its jet axis directed at the ignition point situated at thecenter of the cylinder head.

[0006] Most injection systems known from the publications cited aboveconcern combustion methods with wall-guided or air-guided fuel flow. Theair-guided combustion method depends to a very great extent on themovement of incoming air, which has the function of conveying anignitable fuel-air mixture exactly into the electrode area of the sparkplug over the entire stratified charge operation range of the enginecharacteristics map. In the wall-guided combustion method, fuel iscarried to the spark plug with the support of more or less fracturedcombustion chamber geometries with simultaneous formation of themixture.

[0007] Transport of the mixture to the spark plug is very incomplete inwall-guided and air-guided combustion methods in idling operation and inthe lower partial load range, and in the middle partial load range ofoperation it is possible in part only with unjustifiably lowmanufacturing tolerances of the high-pressure injectors used or the flowguidance through the intake manifold. The inadequate reproducibility isapparent in particular in increased emission of unburned hydrocarbonsdue to isolated instances of misfiring. These properties result inanother serious disadvantage of the two combustion methods mentionedabove: the engine cannot be operated unthrottled in the idling and lowerpartial load ranges because due to the great distance between the fuelinjector and the spark plug, smaller injection quantities no longerreach the spark plug in the mixture concentration required for stablecombustion. This means that the fuel-air mixture at the spark plugelectrodes becomes too lean. However, due to the intake air throttling,the advantage in terms of fuel consumption is reduced in comparison withinternal combustion engines having compression of a mixture with sparkignition and intake manifold injection.

[0008] Advantages of the Invention

[0009] The fuel injection system according to the present inventionhaving the characterizing features of claim 1 or of claim 9 has theadvantage over the related art that the mixture in the area of the sparkplug is not too rich and not too lean due to the design of the injectionholes of the fuel injector there, but instead lean bridges are almostentirely prevented due to an approximately closed conical jet shape. Themeasure according to the present invention supports the development of astable flame core.

[0010] It is also advantageous that the spark plug becomes less sooty,the thermal shock load is reduced, and the lack of sensitivity to thefiring angle is improved with a fixed injection time in the entireengine characteristics map in which stratified charge operation iscarried out. Injection and ignition may thus take place simultaneously.

[0011] The design of elongated injection holes has the advantage thatthe flow losses during the flow through the injection holes are reduced,so the operating pressure may be lowered.

[0012] Advantageous refinements of the fuel injection systemcharacterized in claim 1 and in claim 9 are possible through themeasures characterized in the subclaims.

[0013] Various arrangements of the injection holes and different anglesof inclination relative to one another may be selected, depending on therequirements of the fuel injection system.

[0014] The elongated design of the injection holes enclosing the sparkplug is also especially advantageous because the spark plug or the sparkplug electrodes can be mounted at a variable mounting depth within acertain tolerance, which is predetermined by the length of the injectionholes.

BRIEF DESCRIPTION OF THE DRAWING

[0015] Preferred embodiments of the present invention are schematicallyillustrated in the drawing and explained in greater detail in thefollowing description.

[0016]FIG. 1 shows a schematic section through an embodiment of a fuelinjection system according to the present invention including a fuelinjector,

[0017] FIGS. 2A-B show a first group of embodiments of the design of thevalve body of the fuel injector according to the present invention;

[0018] FIGS. 3A-C show a second group of embodiments of the design ofthe valve body of the fuel injector according to the present invention;

[0019] FIGS. 4A-B show a third group of embodiments of the design of thevalve body of the fuel injector according to the present invention;

[0020] FIGS. 5A-B show a fourth group of embodiments of the design ofthe valve body of the fuel injector according to the present invention.

DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

[0021]FIG. 1 shows a detail of a schematic sectional diagram of alongitudinal section through an internal combustion engine 1 havingcompression of a fuel mixture. Internal combustion engine 1 has acylinder head 2 in which are situated a spark plug 3 and a fuel injector4 in suitably designed recesses. Since the design of both spark plug 3and fuel injector 4 are known in principle, further description of theseparts is unnecessary.

[0022] Fuel injector 4 injects fuel in a conical injection jet 5 into acombustion chamber 7 delimited by cylinder head 2, a piston 6 and acylinder wall (not shown). Combustion chamber 7 is formed in part by acombustion chamber depression 8 formed in piston 6.

[0023] Fuel injector 4 and spark plug 3 are situated relative to oneanother so that spark plug 3 projects into combustion chamber 7 at alateral offset from fuel injector 4, spark plug electrodes 9 beingsituated in the area of injection jet 5.

[0024] The shape of injection jet 5 depend on the design of the sprayend of fuel injector 4. For example, fuel injector 4 is designed as aninwardly opening (I-valve) fuel injector 4. Fuel is injected intocombustion chamber 7 by energizing an electromagnetic or piezoelectricactuator, causing a valve needle (not shown) or a valve closing bodyconnected to it to lift up from a valve body equipped with injectionholes. In this way, fuel is injected into combustion chamber 7 throughfuel injector 4 and the injection holes in the valve body.

[0025] Embodiments of the injection holes in the valve body according tothe present invention are illustrated in FIGS. 2-5 and explained ingreater detail below.

[0026] FIGS. 2-5 each show on the left side a valve body 10 havinginjection holes 11 and on the right side of the respective figures, adeveloped view of injection holes 11 situated on the circumference ofvalve body 10.

[0027]FIG. 2 shows two embodiments of the arrangement of injection holes11, with injection holes 11 being arranged in two rows 12 a, 12 b ofinjection holes 11 or with injection holes 11 displaced out of row 12 a.The other rows each have only two individual injection holes 11 whichare offset out of row 12 a with respect to the spray direction. Bothrows 12 a, 12 b in FIG. 2A have an axial spacing from one another. Onthe side of valve body 10 facing spark plug 3, first row 12 a has aspark plug gap 13, one injection hole 11 a being omitted. Instead ofinjection hole 11 in first row 12 a, two other injection holes 11 b areprovided in second row 12 b to guarantee the homogeneity of injectionjet 5 or the mixture cloud thus formed in combustion chamber 7.

[0028] To achieve further homogenization of injection jet 5, injectionholes 11 may also be arranged with a displacement as illustrated in FIG.2B, so that injection holes 11 c having the greatest displacement arelocated at a distance b from row 12 a. Spark plug gap 13 may be enlargedsomewhat in this way without impairing the homogeneity of the mixturecloud in combustion chamber 7.

[0029] Distances a and b between displaced injection holes 11 may beadapted to the respective requirements in a variable manner.

[0030]FIGS. 3A through 3C show various combinations of round injectionholes 11 and elongated injection holes 11 d. Elongated injection holecross sections have the advantage over round cross-sectional shapes inthat they have a higher flow coefficient, i.e., flow is less disturbedin comparison with round injection holes. Therefore, friction losses andturbulence losses may be reduced and consequently the system pressuremay also be reduced.

[0031]FIG. 3A shows a combination of round injection holes 11 andelongated injection holes 11 d, the round injection holes 11 being inthe same plane with the spray ends of elongated injection holes 11 d.Elongated injection holes 11 d are arranged at the right and left ofspark plug gap 13.

[0032]FIG. 3B shows elongated injection holes 11 d which are alsoinclined with respect to one another by a freely selectable angle,amounting to approx. 45° in the present example.

[0033] As shown in FIG. 3C, round injection holes 11 may also be in aplane with the center points of elongated injection holes 11 d. In allthree cases, a relatively homogeneous mixture cloud may be produced, theinjection quantity being influenceable by the size of injection holes11, 11 d.

[0034] Like FIGS. 3A and 3C, FIG. 4 shows two injection holearrangements where only elongated injection holes 11 d are provided invalve body 10.

[0035]FIG. 4A shows elongated injection holes 11 d arranged as in FIG.3A, so that elongated injection holes 11 d bordering spark plug 3, withtheir spray ends in the same plane with the other elongated injectionholes 11 d′ arranged peripherally on valve body 10 and tilted in theirextent by 90° to injection holes 11 d at spark plug gap 13. FIG. 4Bshows elongated injection holes 11 d′ situated peripherally in one planewith the center points of elongated injection holes 11 d surroundingspark plug 3.

[0036] The arrangements of elongated injection holes 11 d, 11 d′ shownin FIGS. 4A and 4B have the advantage that the manufacturing cost islower because fewer injection holes 11 d, 11 d′ need be provided invalve body 10. A very homogeneous distribution of fuel during injectionis guaranteed by the fact that the periphery of valve body 10 is mostlycovered with elongated injection holes 11 d′.

[0037]FIG. 5 shows two embodiments of an arrangement of elongatedinjection holes 11 e at a tilted angle in comparison with elongatedinjection holes 11 d near spark plug 3.

[0038]FIG. 5A shows elongated injection holes 11 e with their upperinlet ends inclined in the direction of elongated injection holes 11 dnear spark plug 3. The inclination of elongated injection holes 11 e isconfigured so that inclined injection holes 11 e have at least oneparallel main axis. A slight overlapping of the injection jets of theindividual injection holes 11 e may be achieved by additionalinclination of elongated injection holes 11 e, thus further improvingthe homogeneity of the mixture cloud.

[0039]FIG. 5B shows an arrangement similar to that in FIG. 5A, butelongated injection holes 11 e are now inclined in the oppositedirection, i.e., the upper inlet ends of elongated injection holes 11 eare inclined away from elongated injection holes 11 d near spark plug 3.A slight overlapping is also possible here.

[0040] The present invention is not limited to the embodiments presentedhere and it can also be applied to fuel injectors 4 having fewer or moreinjection holes 11, for example. Likewise, elongated injection holes 11may also be situated on more than one rows to thereby improve thehomogeneity of the fuel-air mixture. The elongated design of injectionholes 11 is also not limited to an optimum elliptical shape. Thecross-sectional shapes may also be rectangular or oval.

What is claimed is:
 1. A fuel injection system (1) for internalcombustion engines, comprising at least one fuel injector (4) whichinjects fuel into a combustion chamber (7) having a spark plug (3)projecting into the combustion chamber (7), the fuel injector (4) havinga valve body (10) which has a plurality of injection holes (11) situatedon the circumference so that an at least approximately conical injectionjet (5) is produced in the combustion chamber (7), wherein at least theinjection holes (11 d) situated directly on both sides of the spark plug(3) have an elongated cross-section.
 2. The fuel injection systemaccording to claim 1, wherein the center points of the elongatedinjection holes (11 d) are aligned with the remaining injection holes(11, 11 d, 11 d′, 11 e).
 3. The fuel injection system according to claim1, wherein the ends of the elongated injection holes (11 d) are alignedwith the remaining injection holes (11, 11 d, 11 d′, 11 e).
 4. The fuelinjection system according to one of claims 1 through 3, wherein allinjection holes (11 d, 11 d′, 11 e) have an elongated cross section. 5.The fuel injection system according to one of claims 2 through 4,wherein the injection holes (11 d) situated in the immediate proximityof the spark plug (3) are tilted by a predefined angle relative to theother injection holes (11).
 6. The fuel injection system according toclaim 4, wherein the injection holes (11 d) situated in the immediateproximity of the spark plug (3) have an axially parallel orientation,while all the other injection holes (11 d′, 11 e) have a differentorientation.
 7. The fuel injection system according to claim 6, whereinthe other injection holes (11 d′) are tilted at a 90° angle relative tothe orientation of the injection holes (11 d) in the immediate proximityof the spark plug (3).
 8. The fuel injection system according to claim6, wherein the other injection holes (11 e) have an inclination and aresituated so that one of their main axes is parallel.
 9. A fuel injectionsystem for internal combustion engines, comprising at least one fuelinjector (4) which injects fuel into a combustion chamber (7) having aspark plug (3) projecting into the combustion chamber (7), the fuelinjector (4) having a valve body (10) which has a plurality of injectionholes (11) situated on the circumference so that an at leastapproximately conical injection jet (5) is produced in the combustionchamber (7), wherein at least the injection holes (11 b) situateddirectly on both sides of the spark plug (3) are positioned in a row (12b) which is offset relative to a row (12 a) of the other injection holes11 a).
 10. The fuel injection system according to claim 9, wherein twoinjection holes (11 b, 11 c) on each of the two sides of the spark plug(3) are situated in a stepped pattern in two planes that are offsetrelative to the row (12 a) of the other injection holes (11 a).